Sticking nodes on FSI interface in OpenFOAM/CalculiX coupling

Hello,

I have a problem with sticking nodes on the FSI interface of preCICE 2 and OpenFOAM/CalculiX:

I try to model a valve case with a flexible disc closing a circular orifice by increasing pressure. On the OpenFOAM side I have the problem that 2 nodes stick in their original position directly from the beginning and don’t move with the FSI-interface. In the point-displacement file it seems they get all the time no displacement, even the CalculiX displacements look smooth.

I tried a number of different meshes (element type and resolution) and different mapping options (nearest neighbour and nearest projection). Also I tried with displacements and displacement deltas. In the initial state, the surfaces are plain and geometrical identical (no gap between CCX and OpenFOAM part). Writing out the FSI-interface in vtk from preCICE it is obvious that there are 2 points without displacement as shown on the figure (almost in centre of the disc all time). Any ideas how to fix this?

Thanks

Ulrich

Hello Ulrich,

this problem looks really interesting!

How do you define the interface patch in OpenFOAM? I assume that there is something special about this center point?

Also, do you run in serial or in parallel? If in parallel, where do you split the domain?

Hi Makis,

thanks for the prompt reply.

The interface is just a wall patch with moving wall velocity (U), zeroGradient for pressure and fixed value in fixedValue in pointDisplacement.

Honestly, there is nothing special with this point. This is even not the centre point of the geometry (not 0/0/0).

I ran in serial. I can share this case if you are interested.

Best regards

Ulrich

Indeed, sharing the case would definitely help to understand what is going on.

Have you tried exporting the interface meshes and checking if the mapping is correct? Although I expect this to be some problem in the adapter.

Hi @Ulrich

Could you please upload your vtks? and your preCICE config file. Thanks!

Dear Makis, dear Benjamin,

thanks for the hints. The advice to look more into detail at the interfaces was very valuable.
I think I found the problem: The problem occurred already on the CalculiX side: There was a geometry point defined in the middle of disc, which has been meshed but the node had no element connection. The node was stored in the original CalculiX input file but CalculiX seems to skip this node (as it was not used) during initialisation of the simulation. I didn’t find this nodes listed anymore in the *.frd-file. But it seems the adapter still had this node in the list but zero displacement has obviously been reported to this node (as it was not used in FEA). The zero-displacement node has been used in the mapping to the OpenFOAM mesh which seems to cause the sticking points on the mesh faces. So your adapter works well, I have to get rid of the unused nodes.
I just rerun my simulation and it looks fine so far. If there is interest in this case, I can upload it (maybe after getting it working reliably). But it is rather a demonstration case which does not use physical correct properties
Ulrich

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Great to hear! Thanks for the update.
Sounds like a nice picture for a testimonial? :grin: